JP3002246B2 - Charged beam correction method - Google Patents

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial application field) The present invention relates to a charged beam writing technique for writing a fine pattern such as an LSI on a sample, and in particular, projects onto a sample by a character projection method. And a method for correcting the displacement, rotation, magnification, or astigmatism of the shaped beam.

(Prior Art) Conventionally, as a device for drawing a desired pattern on a sample such as a semiconductor wafer, an electron beam drawing device using a variable shaped beam such as a rectangle or a triangle has been used. In such an electron beam writing apparatus, when writing a fine pattern, the number of figures per unit area increases, so that there is a problem that the writing time increases in proportion to this and the throughput is significantly reduced. As a method of solving such a problem, several types of pattern figures having complicated shapes repeatedly used in an LSI chip or the like are processed and formed on an aperture mask, and each pattern figure on the aperture mask is selectively irradiated with a beam. There has been proposed a drawing apparatus of a system (hereinafter, referred to as a “character projection system”) in which a beam pattern generated by passing through is reduced and projected on a sample.

Examples of the pattern having the complicated shape include a combination of a plurality of rectangles and triangles, and a pattern having an uneven portion.

In such an apparatus, a beam pattern or the like having a complicated shape, such as a combination of a plurality of rectangles and triangles, can be radiated at one time, so that it is possible to greatly speed up drawing.

However, in the character projection method, LSI
In order to draw a pattern, a method of correcting the position, magnification, astigmatism, and the like of a beam having a complicated shape such as a character beam with high accuracy is essential.

As a method of correcting a variable shaped beam, the present inventors have previously proposed Japanese Patent Application No. 1-243313. It is a method of correcting a rectangular or triangular beam from the beam intensity in two orthogonal directions (X direction and Y direction) of the beam pattern. In the case of a shaped beam having a simple shape such as a rectangle or a triangle, it can be corrected by such a method. However, in the case of a shaped beam having a complicated shape such as a character beam, correction cannot be performed with high accuracy by this method.

(Problems to be Solved by the Invention) As described above, although the use of a character projection beam can improve the throughput in forming a fine pattern, a character beam correction technique for obtaining a highly accurate pattern drawing is currently being developed. It was not practical without it. Therefore, there has been a demand for a method for accurately correcting the size, shape, and inclination of a beam having a complicated shape such as a character beam.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a charged beam drawing apparatus that can generate not only a rectangle and a rectangle but also a beam having a complicated shape such as a character beam. An object of the present invention is to provide a charged beam correction method capable of calibrating a beam magnification, rotation, position shift, or astigmatism with high accuracy for the purpose of improving the accuracy of forming a fine pattern.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a beam pattern of the pattern figure by irradiating an aperture mask having at least a repeated pattern figure such as an LSI chip with a charged beam. In a character projection type charged beam exposure apparatus that deflects and deflects a beam at a desired position on a sample, the beam pattern is scanned by scanning the beam pattern a plurality of times over a minute mark on the sample surface. Is two-dimensionally measured, and the electron optical system is corrected according to the amount of shift between the pattern shape and the design data of the aperture on the sample surface.

(Operation) According to the present invention, a two-dimensional distribution (shape) of a character projection beam is obtained, and a graphic process is performed by a computer to match this with the aperture design data, and based on the data obtained as a result. By correcting the electron optical system such as the objective lens, the astigmatism correction coil, and the inclination of the aperture, the character beam can be set to the size, shape, and inclination according to the aperture design data. As a result, highly accurate correction can be performed in a short time even for a beam having a complicated shape such as a character beam.

(Examples) Hereinafter, details of the present invention will be described with reference to the illustrated examples.

FIG. 1 shows a schematic configuration diagram of an electron beam writing apparatus used in the method of one embodiment of the present invention. Reference numeral 10 denotes a sample chamber, in which a sample table 12 on which a sample 11 such as a semiconductor wafer is mounted is accommodated. The sample stage 12 can be moved in the X direction and the Y direction by the sample stage drive circuit 31 that has received a command from the computer 30. Also, the character beam converges the beam from the electron gun 21 with lenses 22a, 22b, etc.
The first aperture 27a is deflected by the deflection system 24.
And by weighing the beam at 27b. The deflectors 25 and 26 are configured by beam scanning deflectors for scanning the character beam on the sample 11 by a deflection signal from the deflection control circuit 33.

In the sample chamber 10, an electron detector 37 for detecting reflected electrons and the like from the sample 11 is provided. This electronic detector 37
Is used to detect reflected electrons from a mark of a fine gold particle located on the sample 11. This mark can be of any material and shape as long as the beam shape can be measured by the reflected electrons of the irradiated beam.

Next, the character projection beam system will be described with reference to FIGS. 1st aperture
27a has a rectangular hole. The image of this hole can be formed at an arbitrary position on the second aperture 27b of the character aperture by the lens 22c and the shaping deflector 24. Since a plurality of characters 30a to 30d, which are frequently used in an LSI chip, are machined on the character aperture 27b, the beam is shaped into a desired character, here 30a, by changing the beam deflection direction by the shaping deflector 24. By irradiating a desired position on the sample 11 with the formed character beam deflectors 25 and 26, an LSI pattern can be drawn at high speed. Reference numeral 30e denotes an aperture for forming a rectangular or triangular beam by superimposing the beam with the rectangular aperture 27a.

In an apparatus of such a type, when the voltage of the deflectors 25 and 26 is constant, the irradiation position on the sample changes greatly depending on the shape of the character beam. Therefore, it is necessary to define a fixed point (reference position of the beam) of each character beam, and determine a different offset voltage (return voltage) for each character beam so that the fixed point coincides on the sample surface.
The present invention is extremely effective also in determining the return voltage.

Next, an embodiment of a beam correction method according to the present invention will be described.

A method for measuring the two-dimensional distribution of the character beam will be described with reference to FIGS. First of all, the deflector shown in Fig. 1
With the offset voltage of 25 and 26 set to 0 volt, a character beam 30 is formed on the sample surface 11, and this beam is
Scan in the X direction on 31. Next, the beam is shifted by a small amount in the Y direction by the deflectors 25 and 26, and the beam is again scanned in the X direction. By repeating such scanning, a two-dimensional distribution of the character beam shape as shown in FIG. 4A can be obtained. However, since the resolution of the beam is limited here, the edge of the measured beam has a blurred shape as shown in FIG.

Therefore, the edge of the beam is determined by binarizing it with a certain threshold (for example, the beam intensity at which the resist on the sample is exposed). As a result, measurement data of the beam shape as shown in FIG. 4 (b) is obtained.

FIGS. 5A and 5B show the actually measured beam shape data and aperture design data, respectively. The aperture design data is design data of the size, shape, inclination, and position of the character beam on the sample. Point A is called a fixed point and is a reference for the position of the character beam. The difference between the measured data and the aperture design data is that the rotation of the second aperture 27b, the magnification of the objective lens, the astigmatism coil, and the return voltage of the deflectors 25 and 26 in FIG. 1 are not set to the correct values. That's why.
Therefore, processing for matching the measurement data with the aperture design data is performed by a computer, and the magnification, distortion (shape) and inclination of the measurement data are detected, and the values are corrected by feeding back to the drawing apparatus.

Specifically, first, the design data A in FIG. 5 and the measured data A 'are made to coincide with each other on a computer. This is a deflector
By applying a return (offset) voltage corresponding to each character beam to 25 and 26, they can be matched. Similarly, the amount of rotation angle correction required for the second aperture 27b can be determined from the relatively long line segment in the character, for example, the angle between the line segment AB and the line segments A 'and B'. Further, the amount of magnification correction required for the objective lens can be determined from the difference in length. At this time, the vertices (for example, vertices C and C ′) of the aperture design data and the measurement data may not match due to the astigmatism of the optical system. The direction and amount can be determined. By feeding back the correction amounts thus obtained to the drawing device, even a beam having a complicated shape can be set with high accuracy, and as a result, the drawing accuracy can be improved.

In the above embodiment, the method of binarizing the measurement data to determine the edge of the beam has been described. However, the measurement data is not binarized, and the position, magnification, and rotation of the aperture design data are changed. The correlation may be obtained, and the point at which the correlation becomes maximum may be determined as the position, magnification, and rotation angle of the measured beam. In this case, as to the astigmatism condition, the amount of astigmatism can be determined by performing a process of blurring the aperture design data by changing the way of blurring in the direction of astigmatism generation and calculating a correlation with the blurring process.

In addition, if the above-described correction method is applied to a normal rectangular beam, the correction accuracy can be further improved, and it goes without saying that the correction method can be applied to a drawing apparatus having one or a plurality of shaping apertures.

In addition, it is also possible to perform measurement again based on the result of the feedback, perform the same processing, perform more detailed adjustment, and obtain further improvement in accuracy.

As described in detail above, according to the embodiment of the present invention, the sample is exposed to the beam of any shape including a rectangle and a character projection beam in real time without experimentally exposing the sample and observing the sample with the SFM. size,
The shape and inclination can be set with high accuracy.

[Effects of the Invention] According to the present invention, it is possible to easily improve the pattern drawing accuracy in a charged beam drawing apparatus of the character beam projection system.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an electron beam drawing apparatus used in a method of one embodiment of the present invention, FIG. 2 is a schematic diagram for explaining a character projection beam system, and FIG. 3 is a beam of an embodiment of the present invention. Schematic diagram for explaining a scanning method,
FIG. 4 is a schematic diagram showing the measured beam intensity distribution and binarized measurement data, and FIG. 5 is a schematic diagram showing a method of comparing the measurement data with the aperture design data. 10 ... Sample chamber, 11 ... Sample, 12 ... Sample table, 20 ... Electronic optical column, 21 ... Electron gun, 22a-22e ... Lens, 23-26
…… Deflector, 27a, 27b …… Aperture for beam shaping, 30
... Computer, 31 ... Sample stage drive circuit, 32 ... Laser length measuring instrument, 33 ... Deflection control circuit, 34 ... Blanking control circuit, 35 ... Variable shaping beam size control circuit.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-59-161818 (JP, A) JP-A-63-237526 (JP, A) JP-A-1-147831 (JP, A) JP-A-3-3 188616 (JP, A) JP-A-4-71219 (JP, A) JP-A-3-232217 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/027

Claims (4)

(57) [Claims] 1. A character projection for irradiating a charged beam onto an aperture mask having at least a repeated pattern graphic such as an LSI chip or the like to form a beam pattern of the pattern graphic, deflecting the beam pattern and drawing the beam pattern at a desired position on a sample. In a charged beam exposure apparatus of the system, the beam pattern
The beam pattern shape is measured two-dimensionally by repeating scanning in which the beam is shifted by a small amount in the Y direction and then scanning in the X direction again more than once, and the beam shape is measured two-dimensionally. A charged beam correction method comprising: correcting an electron optical system according to a shift amount from aperture design data. 2. The charged beam correcting method according to claim 1, wherein the pattern data obtained by two-dimensionally measuring the pattern shape is binarized, and a deviation amount of the beam pattern is obtained from the binarized data and the design data. . 3. The charged beam correction method according to claim 1, wherein a correlation coefficient between the data of the measured pattern shape and the design data of the aperture is obtained, and a shift amount is obtained from the correlation coefficient. 4. The charged beam correction method according to claim 2, wherein a positional deviation, a magnification, a rotation or an astigmatism of the formed beam is corrected from the deviation amount.